marywest45 was, I believe, diagnosed with thoracic onset of ALS, and also Erica, but the classification was changed to bulbar onset (maybe) for her. Both of these members are very nice, and I'm sure would be more than happy to hear from you. As the thoracic region is the area the diaphragm and intercostal muscles are located, I think this is what would be considered respiratory onset.
Several of us (me included) had breathing issues from the onset, or nearly the onset, but still would not be considered to be in this classification.
When you say you feel like the left side of your diaphragm does not work, what do your doctors say about this? Have you told them? I ask, because I noticed when I read through my pulmonologist's notes from my last appointment, that he had written I did not use accessory muscles to breath (using accessory muscles would not be a good thing by the way). My point being that our doctors observe a lot more during our appointments with them than they may indicate while with us.
Good luck to you, I hope you get some answers SOON!